TEC: The Eyepiece Calculator

Updated September 22, 2011

Copyright, 2011, by David Paul Green, Los Angeles, California, USA

Focal Length of Your Scope in millimeters (FLs)
Aperture of Scope in Inches (APi)
If you know the aperture of your scope in inches, enter it to the left. If you know it in mm, enter it to the right. Make sure the field you don't know is empty or 0.
fRatio of Scope
Aperture of Scope in mm (APm)

Barlow Power

(Enter Barlow Magnification)

Eyepiece Type/Description
(replace with your own)
Eyepiece Focal Length (FLe)
Eyepiece Apparent Field of View (FOV) °
Exit Pupil
(EX=APm/M)
Eyepiece
Power
(M=FLs/FLe)
Eyepiece True Field of View ° (T=FOV/M)
Barlow Factor
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.

Click to see apparent fields of view for common eyepieces: